The invention relates generally to the area of machine controls; and specifically, the invention provides a method and apparatus for selectively executing independent processes during a cycle of operation. The invention may be applied to any type of machinery having a computer based control, however, the preferred embodiment will disclose the application of the invention to a machine tool having a computer numerical control.
The control of a machine tool may be divided into two general areas--a machine slide control and a machine process control. The machine slides control the relative position between the workhead and the workpiece. The relative position is defined by a part program and control is executed by a servomechanism. At different points within a slide positioning cycle, different machine processes may be required, e.g. tool change, spindle start and stop, coolant control, etc. Although synchronized with the machine slide controls, the machine process control is typically an independent process.
For years the logic and operation of machine cycles were controlled by circuits of electro-mechanical relays located with the machine but separate from the numerical control. During the last fifteen years, programmable controllers have been used extensively to replace the relay circuits. Programmable controllers have the advantages of being more reliable, generally less expensive and more flexible in their programming. However, with the increased capabilities of a computer numerical control, many of the machine processes have been integrated into its operation. One approach has been to implement the operation of a programmable controller in the computer numerical control. In this case, special interface circuits are designed which operate in conjunction with the numerical control to emulate the operation of the programmable controller.
Another approach is to design tailored special programs which are operable strictly within the computer numerical control to control many of the dedicated machine functions, e.g. spindle functions, tool change functions, etc. The computer numerical control executes these functions as they are required in a typical part program. However, experience has proven that tailored machine function programs within the numerical control have certain disadvantages. First, many end users require slightly different modes of operation to make the machine tool cooperate with the end users overall manufacturing process. Further, different areas of the United States as well as other countries have differing standards which require modifications in the operation of the machine cycles.
Therefore, an object of the invention is to provide a machine cycle controller which is integrated within the computer numerical control but is more general, more flexible and more easily utilized and changed by the machine tool builder.
Another object of the invention is to provide a wide variety of diagnostic features for specifically monitoring machine signals which are required to execute a particular function as well as other machine signals which result from the execution of the machine functions.
A further object of the invention is to provide a system which only monitors the particular devices on the machine which are required for the execution of a current machine process. This is in contrast to systems which sequentially scan all the devices on the machine on a continuous basis.